The invention relates to a device for automatically controlling the suction power of a vacuum cleaner.
Recently increased efforts have been undertaken to control the suction power produced by for instance household or industrial vacuum cleaners, or else to regulate it by taking into account actual external values which occur upon operation of the vacuum cleaner, since in many cases it is desirable to adapt the suction power produced to the operating conditions and the place of work. Operating a vacuum cleaner with only one speed, for instance at rated power, is seldom in accord with the practical requirements; it is uneconomical and wasteful of energy and permits neither the use of lower suction powers in most cases (for instance when light carpets or drapes are to be vacuumed) nor the use of a higher-power for brief use, should this be necessary or desirable.
In one known embodiment for controlling the vacuum produced by vacuum cleaners, constant rate of passage of the air through the apparatus is established by a small turbine driven by the stream of air of the vacuum cleaner located behind the blower. The turbine produces, in the manner, for instance, of a tachometer, a regulating voltage which is fed to a speed control device for the drive motor of the vacuum-cleaner blower. In this way it is possible to maintain the air flow, and therefore the quantity of air fed, approximately constant regardless of different suction conditions. It is possible for such a device also to respond automatically to an increasing amount of dust in the dust bag of the vacuum cleaner. The provision of a small regulating turbine is, however, very expensive as a result of its construction and it may also lead to problems upon daily use. In particular, the possibility cannot be excluded that the turbine, which lies continuously within the expelled stream of air of the vacuum cleaner, will gradually become clogged by residual quantities of dust or that its efficiency will be impaired by the hotter discharge air of the vacuum cleaner, as a result of which malfunctions of the entire system can then occur due to the closed control loop. Finally, it is not out of the question that upon the operation of a vacuum cleaner, operating conditions will frequently arise which make a merely constant flow of air neither necessary nor desirable. Furthermore, there is the disadvantage that with turbine control one can operate in the widest range only with one given power, so that regulation by means of a turbine driven by the stream of air can also be dispensed with.
In another known type of regulation of the suction power produced by a vacuum cleaner there is present, within the field of suction thereof, for instance in front of the dust bag or at some other suitable point, a diaphragm which is acted on by the vacuum prevailing there. The continuous pressure-dependent displacement of said diaphragm acts on a potentiometer which is a part of the control circuit for regulating the speed of rotation of the vacuum-cleaner motor. Since systems with semiconductor elements, for instance thyristors or the like operating by the phase-lag principle, are customarily used for the speed regulation of motors (the thyristors being connected in series with the supply terminals of the motor), the diaphragm-displaced potentiometer can be placed in the control circuit of the thyristor. Accordingly a given power of the vacuum-cleaner motor can be regulated depending on the existing vacuum. In this known device the regulation is such that with stronger vacuum in the suction region the power of the motor is decreased while with full flow of air and correspondingly low pressure the apparatus produces practically its entire power, as is, for instance, the case upon idling. Such a characteristic curve can also lead to undesired difficulties in other cases of use, for instance if the operator attempts by particulary firm application of the suction brush to obtain a better sealing of the brush with respect to the surface to be cleaned. As a result--as the user well knows--the vacuum conditions in the region of the brush can be increased to such an extent that very strong suctions can be produced which take up even firmly adhering fuzz, threads or the like. The known electronic controls prevent this, however, since in such a case of high vacuum, the power is reduced. Such a design may, however, be advantageous for the vacuuming of high-pile carpets or the like, in which case one cannot expect a strong sealing in the region of the suction and thus the occurrence of a greater vacuum but, on the other hand, a particularly high power is desired. Therefore, the design of the control curve for a given predetermined characteristic is a detrimental limitation since it is not possible in this way to satisfy all demands which exist as to the regulation of the suction power of a vacuum cleaner under different operating conditions.
Accordingly, one object of the present invention is to provide a simplified device for automatically controlling the suction power of vacuum cleaners and one which operates free of complications and with a high degree of reliability. A further object is to provide a vacuum cleaner which utilizes any desired characteristic curve of the suction power as a function of the actual value of the vacuum produced by the apparatus.